Method for modeling a glenoid surface of a scapula, apparatus for implanting a glenoid component of a shoulder prosthesis, and method for producing such a component

ABSTRACT

An apparatus and modeling method of the present invention includes the successive steps of generating cartographic data representative of points belonging to a glenoid surface; distinguishing from among the cartographic data a first group of cartographic data corresponding to a first part of the glenoid surface, the first surface part being situated farthest down in the vertical direction in relation to the scapula; calculating from the first group of cartographic data a first ellipsoid portion that coincides substantially with the first surface part; and obtaining a theoretical glenoid surface from the first ellipsoid portion. By virtue of the theoretical glenoid surface obtained by this method, it is possible to assist the surgeon in optimizing the position of implantation of a glenoid component and to produce a glenoid component “made to measure” for the scapula that is to be fitted with a prosthesis.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.12/489,092, filed Jun. 22, 2009, which claims the benefit of Frenchapplication no. FR 0854092, entitled “GMCAO appliquée à l'épaule”, filedJun. 20, 2008, the complete disclosure of which is hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates to a method of modeling a glenoid surfaceof a scapula. The present invention also relates to a surgical apparatusand a surgical method for implanting a glenoid component of a shoulderprosthesis. The present invention additionally relates to a glenoidcomponent and a corresponding method for producing such a glenoidcomponent.

BACKGROUND

A surgical operation in which the glenoid articular surface of a scapulais replaced by a concave glenoid prosthetic component is a difficultprocedure, particularly because of the ligaments around the shoulder. Ithas been found that, depending on the geometry of the articulationand/or the position of implantation of such a glenoid component, theglenoid component may be at risk of coming loose on account of thechange in forces that are applied to the glenoid component duringsubsequent movements of the shoulder that has been fitted with theprosthesis.

Currently, orthopedic surgeons select a glenoid component from aplurality of implants having geometries, especially sizes, that differslightly from one another. They choose the glenoid component byempirically estimating the position of implantation of the selectedglenoid component by visually assessing the geometry of the glenoidsurface of the patient being operated on. The surgeon seeks to selectthe prosthetic component and implant it on the scapula in such a waythat this component reproduces the original articular glenoid surface ofthe patient. However, this method can be imprecise, in particular, whenthe original glenoid cavity of the patient is too badly damaged toprovide an indicator that can be directly exploited by surgicalobservation.

SUMMARY

In one embodiment, the present invention is a modeling method includingthe successive steps of generating cartographic data representative ofpoints belonging to a glenoid surface; distinguishing from among thecartographic data a first group of cartographic data corresponding to afirst part of the glenoid surface, the first surface part being situatedfarthest down in the vertical direction in relation to the scapula;calculating from the first group of cartographic data a first ellipsoidportion that coincides substantially with the first surface part; andobtaining a theoretical glenoid surface from the first ellipsoidportion.

By virtue of the theoretical glenoid surface obtained by this method, itis possible to assist the surgeon in optimizing the position ofimplantation of a glenoid component and to produce a glenoid component“made to measure” for the scapula that is to be fitted with aprosthesis.

In another embodiment, the present invention is a surgical apparatus forimplanting a glenoid component of a shoulder prosthesis. The apparatusincludes position-finding means for spatially locating a scapula of apatient, mapping means for mapping a glenoid surface of the scapula,modeling means for obtaining a theoretical glenoid surface fromcartographic data of the glenoid surface supplied by the mapping means,first means of determination for determining a spatial position of alower reference point for implanting the glenoid component from thecartographic data obtained at a lower end of the glenoid surface by themapping means, and means of implantation for obtaining a spatialimplantation configuration of the glenoid component from at least thetheoretical glenoid surface and the lower reference point.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an implantation apparatus according to thepresent invention, applied to the scapula of a patient.

FIG. 2 is a cross-sectional view in a frontal plane with respect to thepatient of the scapula during an operation with the aid of theimplantation apparatus of FIG. 1.

FIG. 3 is a cross-sectional view in a frontal plane with respect to thepatient of the scapula during an operation with the aid of theimplantation apparatus of FIG. 1.

FIG. 4 is a cross-sectional view in a frontal plane with respect to thepatient of the scapula during an operation with the aid of theimplantation apparatus of FIG. 1.

FIG. 5 is an elevational view of a glenoid component produced by amethod of production according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of an implantation or surgical apparatus 1according to the present invention used on the scapula S of a patient tobe operated on with a view to implanting a glenoid component. Using thesurgical apparatus 1, a glenoid surface G of a scapula S can be modeledto help the surgeon optimize the position of implantation of a glenoidcomponent and/or to produce a glenoid component that is better adaptedto a scapula that is to be fitted with a prosthesis, especially in thepresence of a glenoid cavity that is in a state of advanceddegeneration. The underlying concept of the present invention is basedon the realization that, in the vast majority of surgical cases, thedegeneration of the glenoid cavity of a patient is often situated in theupper and posterior region of the glenoid surface. Thus, the presentinvention proposes that only the part of the degenerated glenoid surfacesituated farthest down the scapula is used to obtain, by modeling, atheoretical glenoid surface as similar as possible to the glenoidsurface prior to degeneration.

Estimating a theoretical glenoid surface by modeling has advantages inrelation to optimizing the position of implantation of a pre-existingglenoid component and, independently of this, producing a glenoidcomponent specifically adapted to the scapula of a patient. Thus, thepresent invention further relates to a surgical apparatus and a surgicalmethod for implanting a glenoid component of a shoulder prosthesis andto a method for producing a glenoid component for a scapula. Inpractice, the modeling method according to the present invention isimplemented by any suitable means known in the art, and in particular bycomputing means

The surgical apparatus 1 includes a computer 2 linked to a unit foremitting and receiving infrared radiation. The unit includes a sensor 3connected to the computer 2 and an infrared source 4 covering theoperating field, in which the scapula S of a patient to be treated isshown in part. The scapula S is associated generally with tendons andligaments and delimits the glenoid surface G on its lateral surface. Theglenoid surface G shows degeneration, or partial damage by wear onaccount of the advanced age and/or a disease of the patient who is beingoperated on. As will be explained in detail below, the surgicalapparatus 1 is designed to aid a surgeon implanting a prosthetic glenoidcomponent 5 in order to replace the degenerated glenoid surface G. Inthe embodiment shown in FIG. 1, the glenoid component 5 has an overallcup shape and defines an articular face 5A of substantially sphericalgeometry, defining an axis of revolution 5B. The glenoid component 5described above is given only by way of example, and other prostheticglenoid components of different geometries and/or types can be implantedusing the surgical apparatus 1 and in accordance with the surgicalimplantation method described below.

To spatially locate the bone of the scapula S on the computer 2, thesurgical apparatus 1 includes a group of markers 6 which passivelyreturn infrared radiation in the direction of the sensor 3. The group ofmarkers 6 forms a three-dimensional marking system allowing the assemblycomposed of the computer 2 and the sensor 3 to follow the spatialposition and movement of the scapula S. The use of such markers is wellknown in the field of computer-aided orthopedics, for example, asdescribed in document EP-A-1 249 213, such that these markers will notbe further described here.

The computer 2 is also linked to a screen 8 for displaying informationuseful to the surgeon, for example, information relating to the locationof the scapula S. In one embodiment, the screen 8 may be a video screen.The surgical apparatus 1 also includes control means 9, for example inthe form of a pedal, that can be actuated by the surgeon's foot. Thesurgical apparatus 1 also includes other components, the details ofwhich will be given below in an example of how the surgical apparatus 1is used to implant the glenoid component 5. By convention, throughoutthis document, the spatial positioning terms, such as the words “upper”,“lower”, “vertical”, “horizontal” etc., are understood in theiranatomical sense, as if the patient being operated on is standingupright on a plane surface.

In a first step, the surgeon makes a plurality of incisions in the softparts of the patient's shoulder and collects a number of data relating,among other things, to the anatomical geometry of the bone of thepatient's scapula S. To this end, various means of acquisition of thedata are conceivable. By way of example, the surgeon uses a tracer 10whose position is located by an assembly composed of the computer 2 andthe sensor 3 and which is calibrated in advance. The tracer 10 isapplied to various locations on the scapula S, in particular to thewhole of the glenoid surface G. The surgeon, by actuating the controlmeans 9, causes the computer 2 to record the position of the tracer 10.From this data, and in some embodiments, from pre-recorded data relatingto the basic geometry of the scapula of a human being, the computer 2 isable to establish a three-dimensional map of the degenerated glenoidsurface G of the scapula S.

There are other possible ways by which the cartographic data relating tothe anatomical geometry of the glenoid surface G can be acquired, forexample by extracting such data from pre-operative images of the scapulaS of the patient. In one embodiment, the cartographic data can beobtained from scanner images. Such data can also be combined with dataobtained by tracing as described above, and combining the data, whereappropriate, with predetermined data from databases available in thefield of surgery of the shoulder.

At the end of this first step, the computer 2 displays the mappingresults on the screen 8, particularly for visual monitoring by thesurgeon. This display is effected in particular in a frontal plane withrespect to the patient, passing through the mapping points belonging tothe glenoid surface G and respectively situated at the far top and farbottom, as is illustrated in FIG. 2, in which the far bottom and the fartop mapping points are designated by P₁ and P₂, respectively.

FIG. 2 shows, in an exaggerated manner designed to facilitateunderstanding of the present invention, that the degeneration of theglenoid surface G is essentially situated in the upper part of theglenoid surface, particularly in the upper third of the glenoid surface.By way of comparison, the glenoid surface prior to degeneration isindicated by broken lines and by the reference sign “g”. Comparison ofthe respective outlines of the surfaces g and G in the plane of FIG. 2reveals that the surface G has undergone a degree of degeneration bywear that is much more pronounced in its upper part than in its lowerpart, which remains almost intact.

In a second step, the surgeon controls the computer 2 such that itprocesses the cartographic data obtained during the first operatingstep. Data processing means integrated in the computer 2 processes thecartographic data in a manner that is entirely pre-established, or inaccordance with parameters chosen at the discretion of the surgeon, insuch a way as to distribute the mapping points of the glenoid surface Ginto three distinct groups G₁, G₂ and G₃ which correspond to respectiveparts of the glenoid surface G and which succeed one another in avertical direction from bottom to top. For example, the three surfaceparts G₁, G₂ and G₃ have an identical vertical dimension.

Each of the three groups of cartographic data related respectively tothe surface parts G₁, G₂ and G₃ are then processed independently by theaforementioned data processing means in order to model an imaginaryellipsoid portion G′₁, G′₂ and G′₃, which is indicated by broken linesin FIG. 2 and coincides geometrically with the corresponding surfacepart G₁, G₂ and G₃. In practice, the position of the center C′₁, C′₂ andC′₃ and the value of the radius r′₁, r′₂ and r′₃ of each ellipsoidportion G′₁, G′₂ and G′₃, respectively, are calculated by theaforementioned data processing means in such a way that the ellipsoidportions G′₁, G′₂ and G′₃ passes through the largest number of mappedpoints for the corresponding surface part G₁, G₂ and G₃, respectively.Each of the ellipsoid portions G′₁, G′₂ and G′₃ is regarded as passingthrough one of the mapped points when the multidirectional deviationbetween the ellipsoid portion G′₁, G′₂ and G′₃ and the point is zero,or, at the very least, less than a predetermined value. Othermathematical methods for determining the geometric characteristics ofthe ellipsoid portions G′₁, G′₂ and G′₃ can alternatively be employed.In one embodiment, ellipsoid portions G′₁, G′₂ and G′₃ are spherical.

The computer 2 displays on the screen 8, for the attention of thesurgeon, all or some of the modeled ellipsoid portions G′₁, G′₂ and G′₃,in particular their centers C′₁, C′₂ and C′₃, at the same time asdisplaying the map of the degenerative glenoid cavity as shown in FIG.2.

It will be noted that in so far as the lower surface part G₁ andintermediate surface part G₂ are not degenerated or are only slightlydegenerated, the centers C′₁ and C′₂ of their associated ellipsoidportion G′₁ and G′₂, respectively, obtained by modeling are very closeto each other compared to the center C′₃ of the ellipsoid portion G′₃modeled from the upper surface part G₃.

In a third step, particularly after the surgeon checks the modelingresults hitherto obtained and displayed on the screen 8, checking inparticular that the modeled centers C′₁ and C′₂ are indeed close to eachother by comparison to the center C′₃, the data processing means of thecomputer 2 constructs, by calculation, a spherical theoretical glenoidsurface G′, which is centered on a center C′ and which has a radius r′,of which the position and value, respectively, are calculated from thepositions of the centers C′₁ and C′₂ and from the values of the radiir′₁ and r′₂. By way of example, as is illustrated in FIG. 3, the centerC′ is calculated as the center of mass of the centers C′₁ and C′₂, whilethe radius r′ is calculated as the mean of the radii r′₁ and r′₂. Moregenerally, an essential point of the present invention is that this stepuses the modeled geometric data for the region of the glenoid surface Gthat shows the least degeneration, or the least wear, such as the lowersurface part G₁ and intermediate surface part G₂. In this way, it willbe appreciated that the theoretical glenoid surface G′ thus calculatedcorresponds to a reliable estimation of the whole glenoid surface priorto degeneration. It will also be appreciated that it is possible inpractice to omit calculating the geometric characteristics of theellipsoid portion G′₃ if not displaying the latter on the screen 8 andnot comparing it to the ellipsoid portions G′₁ and G′₂.

The computer 2 then determines the point of intersection between thistheoretical glenoid surface G′ and the straight line radial to theglenoid surface G′ and passing through the mapping point P₂, that is tosay the straight line passing through the points C′ and P₂. As is shownin FIG. 3, this point of intersection is designated by P_(up). It willbe appreciated that this point P_(up) corresponds to a reliableestimation of the upper end point of the glenoid surface prior todegeneration g. The point P_(up) is displayed by the computer 2 on thescreen 8 for visual monitoring by the surgeon.

In a fourth step, the computer 2 provides the surgeon with a display onthe screen 8 that shows a plane of implantation W of the glenoidcomponent 5 (shown in FIG. 1), the line of which can be seen in FIG. 4passing through the aforementioned point P_(up) and also through a pointP_(down) determined by the computer 2. The point P_(down) advantageouslycorresponds to the mapped point P₁.

It is significant that the plane of implantation W corresponds to aparticular plane for implanting the glenoid component 5, in the sensethat it assures the surgeon that the biomechanical behavior of theglenoid component 5 will be substantially similar or identical to thebehavior of the glenoid surface G prior to degeneration if the glenoidcomponent 5 is positioned in such a way that its axis 5B (shown inFIG. 1) extends perpendicular to this plane of implantation W.

If the two points P_(up) and P_(down) on their own are insufficient toprovide all the spatial characteristics of the plane of implantation W,the computer 2 can for this purpose use information directly supplied bythe surgeon or can spatially orientate the plane W passing through thepoints P_(up) and P_(down) using the Lévigne angle, by integrating adatabase relating to the definition of this angle into the computer 2,which data is available from literature on orthopedics.

Thus, the method for modeling a glenoid surface of a scapula includesthe successive steps of: generating cartographic data representative ofpoints belonging to the glenoid surface that is to be modeled;distinguishing from among the cartographic data a first group ofcartographic data corresponding to a first part of the glenoid surface,this first surface part being situated farthest down in the verticaldirection in relation to the scapula S; calculating from the first groupof cartographic data a first imaginary ellipsoid portion that coincidessubstantially with the first surface part; and obtaining a theoreticalglenoid surface from the first ellipsoid portion. In one embodiment, thetheoretical glenoid surface is composed of the first ellipsoid portion.

According to other embodiments, individually or in combination: fromamong the cartographic data, one or more groups of cartographic dataother than the first group of cartographic data are distinguished whichcorrespond respectively to as many surface parts of the glenoid surfacethat are distinct from the first surface part and that are arranged, inthe vertical direction relative to the shoulder blade, following on fromthis first surface part and, if appropriate, one after another; one ormore imaginary ellipsoid portions other than the first ellipsoid portionare calculated from the other group or groups of cartographic data, theother ellipsoid portion or portions coinciding substantially with thecorresponding other surface part or surface parts; the theoreticalglenoid surface is obtained from the first ellipsoid portion and from atleast one of the other ellipsoid portions; in the case where the firstellipsoid portion and the other ellipsoid portion or portions correspondto sphere portions, each sphere portion is determined by calculating theposition of its center and the value of its radius; the theoreticalglenoid surface is spherical, the position of its center and the valueof its radius being calculated respectively as the center of mass of thecenters and the mean of the radii of the first ellipsoid portion and atleast one of the other ellipsoid portions corresponding to the surfacepart or parts situated farthest down; and the first ellipsoid portionand the other ellipsoid portion or portions are determined bycalculating the spatial characteristics of each ellipsoid portion insuch a way that the ellipsoid portion includes, with a presetmultidirectional deviation, the largest number of points of the glenoidsurface which are represented by the cartographic data of the group ofdata related to the ellipsoid portion.

FIG. 5 shows a glenoid component 12 of a shoulder prosthesis which,unlike the component 5 shown in FIG. 1, is not a pre-existing part thatis available from a plurality of homothetic implants. The glenoidcomponent 12 includes a solid implant body 14, metallic or synthetic innature, which has an overall cup shape.

One side of the body 14 is designed as an articular, concave face 12Athat articulates with the humerus of a patient and supports inparticular a humeral prosthetic component of the shoulder prosthesis.Most of the articular, concave face 12A, or in this case all of which,defines an articular surface designed to articulate against asubstantially complementary surface (not shown in the figures) which isdelimited either by the anatomical upper end of a humerus or by thehumeral component of the shoulder prosthesis.

On its opposite side, the implant body 14 has a bearing face 12B which,when the glenoid component 12 is implanted, bears directly or indirectlyagainst the osseous lateral end of a scapula S which has been preparedin advance for this purpose. In a manner known to those skilled in theart, the bearing face 12B is provided with means for anchoring theglenoid component 12 in the scapula S, for example in the form of a stem16.

The glenoid component 12 has been “made to measure” for the scapula S inFIG. 1. Thus, the articular face 12A does not correspond to apre-existing standard geometry but instead reproduces the theoreticalglenoid surface G′ provided by the computer 2 in the third operatingstep mentioned above. As the theoretical glenoid surface G′ is areliable estimation of the glenoid surface prior to degeneration, itwill be appreciated that the articular face 12A is substantiallysimilar, from a geometrical point of view, to the degenerated surface,which explains the use of the aforementioned expression “made tomeasure”. The articular behavior of the glenoid component 12 on itsarticular face 12A is therefore almost identical to the natural behaviorof the patient's shoulder prior to the degeneration of the scapula S.

Advantageously, the bearing face 12B also no longer corresponds to apre-existing standard geometry but instead takes into account the stateof degeneration of the glenoid surface G of the scapula S. Inparticular, the upper end part of the bearing face 12B is designed totake into account the pronounced wear in the upper part of the glenoidsurface G. To do this, the thickness of the implant body 14, that is tosay its dimension in a medio-lateral direction, is greater in the upperend part of the implant body 14 than in the rest of the implant body 14.The maximum value of the thickness at the upper end part of the implantbody 14 being indicated by “e” in FIG. 5. The variation in thickness ofthe implant body 14 is determined, for example with the aid of thecomputer 2 from the cartographic data corresponding to the highestsurface part G₃ (shown in FIG. 2). In this way, when the lateral end ofthe scapula S is prepared with a view to implantation of the glenoidcomponent 12, the surgeon removes only a limited amount of bonesubstance from the lower region of the glenoid surface G, here in thearea of the surface parts G₁ and G₂ (shown in FIG. 2). The amount ofbone removed is just enough to take into account the small thickness ofthe lower part of the implant body 14, whereas the thickness of theupper part of the implant body 14 is dimensioned so as to substantiallymatch the surface part G₃. In other words, contrary to conventionalpractice, the surgeon does not attempt to “level” the upper and mostbadly worn region of the glenoid surface G during its preparation, asthis would lead to excessive removal of healthy areas of bone from thescapula S and would medialize the glenoid component 12, unless theimplant body 14 were made thicker.

In practice, the material forming the glenoid component 12 is shaped byany technique known in the art. In the case of a glenoid component madeof metal, the glenoid component can be cast and then machined. If aplastic is used, it is generally cast and then, if appropriate,rectified. In all cases, the articular face 12A and bearing face 12B areprecision-worked in order to adjust them respectively to the theoreticalglenoid surface G′ and to the prepared lateral end of the scapula S.

The present invention relates to a surgical apparatus for implanting aglenoid component of a shoulder prosthesis including: position-findingmeans for spatially locating the scapula of a patient being operated on;mapping means for mapping the glenoid surface of the scapula; modelingmeans for implementing the modeling method defined above and therebyobtaining a theoretical glenoid surface from the cartographic data ofthe glenoid surface obtained by the mapping means; first means ofdetermination for determining the spatial position of a lower referencepoint for implanting the glenoid component from the cartographic dataobtained at the lower end of the glenoid surface by the mapping means;and means of implantation for obtaining a spatial implantationconfiguration of the glenoid component from at least the theoreticalglenoid surface and the lower reference point.

Thus, by virtue of the theoretical glenoid surface obtained by themodeling method defined above and also by virtue of information thatrelates to a lower reference point that the surgeon can obtain directlyfrom the, in principle, undamaged lower end of the degenerated glenoidsurface of the patient, the surgeon can base the implantation of aglenoid component on data that is satisfactory with regards to thegeometry of the glenoid surface of the patient prior to degeneration.The surgeon is thus able to improve the implantation configuration ofthe glenoid component and is able to do so during the surgicalintervention.

In embodiments of the surgical apparatus of the present invention, thefollowing may be used individually or in combination: a second means ofdetermination for determining the spatial position of an upper referencepoint for implanting the glenoid component from cartographic dataobtained at the upper end of the glenoid surface by the mapping meansand from the theoretical glenoid surface; a means of implantationadapted to obtain the spatial position of a plane of implantation of theglenoid component which passes through the upper and lower referencepoints; the second means of determination adapted to position the upperreference point at the intersection between the theoretical glenoidsurface and a straight line radial to the surface, passing through thepoint of the glenoid surface mapped by the mapping means and situatedfarthest up; and display means for displaying the glenoid surface mappedby the mapping means, the lower reference point and at least somegeometric characteristics of the theoretical glenoid surface, and also,if appropriate, the upper reference point and the plane of implantation.

The present invention also relates to a surgical method for implanting aglenoid component of a shoulder prosthesis in which: the scapula of apatient being operated on is located spatially; the glenoid surface ofthe scapula is mapped using data acquired by tracing the scapula and/orby data extracted from pre-operative images and/or data obtained from apre-established database; the glenoid surface is modeled in accordancewith the modeling method defined above in such a way that a theoreticalglenoid surface of the scapula is obtained from the cartographic data;the spatial position of a lower reference point for implanting theglenoid component is determined from the data associated with themapping of the lower end of the glenoid surface; and the glenoidcomponent is implanted in a spatial configuration determined from atleast the theoretical glenoid surface and the lower reference point. Thesurgical method can be implemented by the implantation apparatus definedabove.

The present invention also relates to a method for producing a glenoidcomponent of a shoulder prosthesis for a scapula in which the glenoidsurface of the scapula is modeled in accordance with the modeling methoddefined above, and in which the articular face of an implant bodydesigned to articulate against a substantially complementary humeralsurface is shaped in such a way that at least part of the articular facereproduces the theoretical glenoid surface supplied by the modelingmethod.

The production method according to the invention allows a glenoidimplant to be “made to measure”, in the sense that its articular facereproduces as closely as possible the glenoid surface, prior todegeneration, of the scapula that is to be fitted with a prosthesis. Thearticular comfort for the patient is thus enhanced.

Of course, it is advantageously possible to produce a glenoid component“made to measure” by means of the method of production according to thepresent invention, and then to implant the glenoid component with theaid of the implantation apparatus defined above, that is to say inaccordance with the method of implantation also defined above.

Various configurations and alternatives of the implantation apparatus,of the implantation method and of the method for producing the glenoidcomponent are also conceivable and are described below. By way ofexample:

-   -   the means for finding the position of the bone of the scapula        and/or of the tracer is not limited to markers that reflect        infrared, markers sensitive to ultrasound or to electromagnetic        fields can be used;    -   it is possible to model only a single ellipsoid portion which        coincides substantially with the lowest part of the glenoid        surface and which will then constitute, for the purposes of the        method, the theoretical glenoid surface;    -   the act of determining the plane of implantation W can be made        optional when the computer is capable of spatially guiding a        tool for implanting the glenoid component shown in FIG. 1 such        that the articular surface of the glenoid component is        positioned in line with the theoretical glenoid surface, taking        into account the lower reference point;    -   the vertical extent of only the lowest glenoid surface part or        that of each of the different glenoid surface parts succeeding        one another from bottom to top can be pre-established, chosen        arbitrarily by the surgeon by indicating it to the computer, or        can be calculated by the computer, especially by a formula of        the ratio between the extent of the part in question and the        total extent of the glenoid surface; and/or    -   more than three imaginary ellipsoid portions can be modeled from        as many successive surface parts along the degenerated glenoid        surface, the spherical theoretical glenoid surface making it        possible to determine the spatial position of the upper        reference point calculated from only the group or groups of        cartographic data corresponding respectively to the lowest        surface part or the lowest surface parts.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the above described features.

The following is claimed:
 1. An apparatus comprising: means forobtaining cartographic data from various locations on a scapula; a dataprocessor that generates a glenoid surface model from cartographic dataof the scapula supplied by the cartographic data obtaining means andpre-recorded data relating to a basic geometry of a human scapula, thecartographic data is representative of a first portion of the glenoidsurface away from a more degenerated area of the glenoid surface of thescapula; wherein the data processor determines a thickness in a portionof a glenoid component corresponding to a second portion of the glenoidsurface from the glenoid surface model and the cartographic data of theglenoid surface.
 2. The apparatus of claim 1, wherein the cartographicdata obtaining means comprises a tracer and a three-dimensional locatingsystem.
 3. The apparatus of claim 1, wherein the cartographic dataobtaining means comprises an image scanner to generate preoperativeimages of the glenoid.
 4. The apparatus of claim 1, wherein the glenoidsurface model is generated solely from data corresponding to the firstportion of the glenoid surface.
 5. The apparatus of claim 4, wherein thethickness is calculated as a difference between a medio-lateral locationof the glenoid surface in a more worn portion of the glenoid and amedio-lateral location of a corresponding portion of the glenoid surfacemodel.
 6. The apparatus of claim 1, wherein the first portion of theglenoid surface is situated farthest down in the vertical direction inrelation to the scapula.
 7. The apparatus of claim 1, wherein the moredegenerated area of the glenoid surface of the scapula is situated in anupper and posterior region of the glenoid surface.
 8. The apparatus ofclaim 1, wherein the second portion corresponds to the more degeneratedarea of the glenoid surface.
 9. The apparatus of claim 1, furthercomprising a display for displaying the glenoid surface model.
 10. Theapparatus of claim 1, wherein the data processor is configured determinea spatial position of a plane of implantation of the glenoid component.11. The apparatus of claim 10, wherein the spatial position of the planeof implantation of the glenoid component passes through the firstportion of the glenoid surface and the more degenerated area of theglenoid surface.
 12. The apparatus of claim 1, wherein the dataprocessor determines the thickness in the second portion of the glenoidcomponent by determining a point of intersection between the glenoidsurface model and a straight line passing through a mapping pointcorresponding to the more degenerated area of the glenoid surface. 13.An apparatus comprising: means for obtaining cartographic data fromvarious locations on a scapula, the cartographic data is representativeof a first portion of the scapula away from a more degenerated area ofthe glenoid surface of the scapula; a data processor programmed tocalculate an imaginary ellipsoid portion from the cartographic datarepresentative of the first portion of the glenoid surface andpre-recorded data relating to a basic geometry of a human scapula,wherein the data processor is programmed to generate a glenoid surfacemodel based at least in part on the imaginary ellipsoid portion.
 14. Theapparatus of claim 13, wherein the data processor is programmed todetermine a thickness in a portion of a glenoid component correspondingto a second portion of the glenoid surface from the glenoid surfacemodel and the cartographic data of the glenoid surface.
 15. Theapparatus of claim 13, wherein the cartographic data obtaining meanscomprises a tracer and a three-dimensional locating system.
 16. Theapparatus of claim 13, wherein the cartographic data obtaining meanscomprises an image scanner to generate preoperative images of theglenoid.
 17. The apparatus of claim 13, wherein the glenoid surfacemodel is generated solely from cartographic data corresponding to thefirst portion of the glenoid surface.
 18. The apparatus of claim 13,wherein the first portion of the glenoid surface is situated in aninferior direction in relation to the scapula.
 19. The apparatus ofclaim 13, wherein the more degenerated area of the glenoid surface ofthe scapula is situated in an upper and posterior region of the glenoidsurface.
 20. The apparatus of claim 13, further comprising a display fordisplaying the glenoid surface model.
 21. The apparatus of claim 13,wherein the data processor is programmed to determine a spatial positionof a plane of implantation of the glenoid component.
 22. The apparatusof claim 21, wherein the spatial position of the plane of implantationof the glenoid component passes through the first portion of the glenoidsurface and the more degenerated area of the glenoid surface.